Facilitating human to machine interactions in a natural manner is a difficult problem. Both non-voice and certain voice interfaces tend to be overly structured and require some level of familiarity with the interfaces. An ability for a human to interact with machines using natural language utterances in various contexts remains a desirable goal. However, human interaction with machines in various contexts can create a cognitive load that may interfere with other tasks, such as operating a vehicle. Thus, a system's determining when system-human conversation should be delayed, prevented or otherwise altered would be desirable.